1. Field of the Invention
The invention relates to a multi-actuation MEMS switch.
2. Description of the Related Art
The wireless communication standards have more than seven types today including GSM, Bluetooth, CDMA and WiMAX, etc. Each communication standard has specific characteristics such as frequency and band width. This means communication modules are more and more complex, and higher frequency band is used to satisfy the new necessary. Comparing to diode or transistor, elements fabricated by micro electro mechanical systems (MEMS) technology can provide better radio frequency (RF) performance at Giga Hertz (GHz) applications. Thus, if RF MEMS elements and other electric elements could be integrated as a communication module via complementary metal-oxide-semiconductor (CMOS) technology, size and cost of communication modules can be reduced.
RF switch has numerous applications in RF circuits. For example, switching RF signal through one block to another, or changing RF blocks characteristics directly by switching a capacitor in a tuning network. A well designed RF MEMS switches should demonstrate several characteristics including low actuation voltage, low power consumption, high switching speed, low insertion loss, high isolation, and reliability.
FIG. 1 is a schematic view of MEMS switch, which are drawings of U.S. Pat. No. 6,486,425. The conventional MEMS switch comprises a glass substrate 31, a metal layer 32, two protrusions 33 and 34, two fixed electrodes 35 and 36, a movable terminal 37, and two fixed terminals 38 and 39. The MEMS switch uses the protrusions 33 and 34, and two fixed electrodes 35 and 36 to apply voltage to generate electrostatic force. Thus, the movable terminal 37 is connected to the fixed terminals 38 and 39 and static electricity is driven by higher driving voltages.
FIG. 2 is a schematic view of another MEMS switch, which are drawings of U.S. Pat. No. 6,927,352. A micro switch 10 comprises a silicon oxide layer 11, a beam 12, two heating elements 13 and 14, four complementary electrodes 15, 16, 17 and 18, a contact pad 19, two conductive tracks 20, and 21, a cavity 22 and two metal portions 23 and 24. The heating elements 13 and 14 are located in the beam 12. There are several additional MEMS processes are necessary to form the metal portions 23, 24, which form with underlying membrane and work as bimetal. To turn on switch 10, a current is run through heating elements 13, 14. The heat released by Joule effect causes a deformation of beam 12 that tends to come closer to the conductive tracks 20, 21. The deformation is due to the expansion difference between metal portions and beam 12. The expansion difference is sufficient to obtain the buckling of the central portion of beam 12.